Adsorption of gases with a liquidadsorbent slurry



United States Patent ADSDRPTION or GASES WITH A LIQUID- ADSORBENT SLURRY Frank Maslan, Newton Highlands, Mass., assignor to Escambia Chemical Corporation, Pace, Fla., a corporation of Delaware 4 Claims. (Cl. 183-1141) This invention relates to the production of chemicals and in particular to the separation or recovery of chemicals from gaseous mixtures. This application is a division of copending application Serial No. 584,186, filed May 11, 1956.

A principal object of the present invention is to provide an improved adsorption process for the separation of chemicals from gaseous mixtures.

Another object of the invention is to provide a liquid adsorption system which has many additional advantages over the currently employed adsorption systems.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

Adsorption is usually carried out by passing a mixture of gases over an adsorbent such as charcoal. The adsorbent may either be a stationary bed or a moving one. The adsorbent will adsorb varying amounts of the gases present in the mixture depending on their characteristics. Basically adsorbents such as charcoal will adsorb high-molecular-weight, low-volatility compounds in preference to low-molecular-weight, high-volatility ones.

Adsorption, when used as a gaseous separation process, has some very definite advantages. First, it is possible to get a very high recovery efiiciency. For example, better than 95 percent of the propane contained in a methane stream can be recovered without much difiiculty. Concurrently, only 5 to percent of the methane would be adsorbed. Second, the adsorption process is highly selective. This is illustrated by comparison of the percentages of propane and methane given in the previous example. This high degree of selectivity enables one to make a sharp separation. Third, comparatively low pressures are required in the adsorption process. These pressures are usually lower than for comparable solvent absorption processes. An adsorbent such as activated charcoal is capable of adsorbing as much as percent of its weight of a material such as propane at pressures of 50 p. s. i. g. and less. Fourth, the adsorption process is usually carried out at room temperature. There is little need for refrigeration other than that obtained with cooling water. On the other hand, it is very common for refrigeration to be required in absorption processes in order to obtain a high enough solvent capacity.

Most of the disadvantages of adsorption separation processes lie in the handling requirements for the solid adsorbents. In the fixed-bed adsorber, over-all effi- 'ice ciency is low because all the adsorbent can not be utilized and because the process is inherently a batch operation. The moving-bed type adsorption process requires large-scale, expensive equipment and has a fairly high attrition loss of the adsorbent. This attrition problem is probably the chief drawback to using any kind of moving adsorbent bed. In this process, particles about inch diameter are usually used. As they move down the tower, they grind on each other, creating a certain amount of fines which have to be separated and discarded on recycle. Since adsorbents are quite expensive, these fines represent a significant percent of the operating cost. The fluidized-bed type adsorption has an even worse attrition problem. In this type of operation, the adsorbent has a usual mesh. size of to 200 and is fluidized with the gaseous mixture so that it flows countercurrent to the gas through a contacting device. As it does so, the adsorbent grinds on itself, producing a very high percent of attrition. For many gaseous separation processes, it is desirable to operate at elevated pressures. On the other hand, it is difiicult to operate solid-gas contacting units at elevated pressures. This is primarily a problem of maintaining gas-tight seals in solids-handling equipment.

The adsorption processes, whether stationary bed or countercurrent-moving bed, are inherently adiabatic op erations. Due to the heat of adsorption, fairly high temperatures occur where the adsorption is taking place.

Since the amount of gas adsorbed is directly related to The present invention is primarily directed to a proc ess for separating, recovering or purifying gaseous mixtures containing a gas or gases which can be adsorbed on an adsorbent by contacting the gaseous mixture with an adsorbent suspended in a liquid, the adsorbent and liquid being mutually incompatible. In one preferred embodiment of the invention, the liquid is water and the adsorbent suspended therein is charcoal, preferably activated charcoal. In another embodiment of the invention, a liquid-adsorbent slurry can be used for the separation of gases soluble in the liquid from gases which can be adsorbed on an adsorbent.

The present adsorption separation process has all the advantages of the adsorbent systems described above and yet eliminates most of the disadvantages found therein. Basically the present invention provides an improved adsorption medium which consists of an adsorbent suspended in a liquid so as to form a slurry. For example, fine-size activated charcoal can be suspended in Water. Hydrodynamically this decreases, almost completely the attrition of the particles on eachother.

than air that each particle of adsorbent is shielded from the other particles by a layer of liquid. This" marked decrease in attrition eliminates the main economic reason for not using fluid-bed adsorption proc esses. Depending on the system of adsorbent and liquid, a wetting agent may be used in order to get better contact between the liquid and the adsorbent. This will depend upon the specific system employed.

The present adsorption process is operable if the gaseous mixture to be treated can diffuse through the liquid and if the liquid and adsorbent are mutually incompatible. This is true of charcoal and water. Char coal will preferentially adsorb organic materials rather than water. On the other hand, such materials as acti- This is due to the fact that the liquid, such as, water, has a viscosity and surface tension so much higher vated alumina and silica gel are hydrophilic. In separating organic gases, the most useful syst'e'rr'i'is activated carbon or charcoal suspended in water.

Not only is th e attrition of the adsorbent decreased by us ing 'theliquid but 'a' slurry is 'n'iu'chieasier to handie than a gassolidfrnixturel The slurry islilge a liqu id and rriay be pumped. Since thelslu'r'ry is like na li qguid, it 'can 'behhandled easily at elevated pressures. Equipment and s'eal shor'dinarily used forlgas liql "systems can easily be used forthe'igafs- 'slurry,systerris d scussed here. In a fluidized bed syste m, large quantities" of gas ,are required tormoving the fliiidirz'ld adsorbentl Thisreq nireri lent is entirely eliminated byIU in gZthe fslurry. The liqiiid (water) will act ,as' 'a coolant "for the heatofad- This means "that thef'teinperature of a dsorpan be 'fcoritrollfedIto'iclsirable lower temperatures. This can mama large nitrerenc'e in the adsorption Gapacity' ofa material such as (charcoal.

' -1 he rich adsorhentiii the slurry "may be.;,regpe ra te d byfone of several means or,6oinbinationsIthereof. @The ambient pressure may'lbe decreased. Thi s causes ;the adsorbate to come oil of ,the adsorbent. ,The slurry maybeboiled. This is a yeryfconvenient of retfainingthe'slurry' and, at theflsarne'time, raising III" perature of the system ,so as", to cause a the arise.rbled gas to coirie 01f; The rich, adsorbent canbejsepa'rated f the liquid'and then heated'to'lashigh a pera'turcas isrequired for regeneration; "Theiisepart ed ad;sor,bent maybe washed ,withfa,solventfwhich 'reinovel I s Qrb ate r the adsorbate may be displaced 1 th another material which is more preferentiallyadsorbedl A comb ina tion of heating anddecreasing?of'Ipress re most preferable regeneration technique.

The present adsorption process may be,used,, -fore,r;- ample, in 'th'e eXtractiQn of ethane and propane from natural gas orr'efin'er'yf gas; This can be easily! plished by contacting natural gas; for1eXan1ple, I slurry of water andtactivated charcoal atllroomlrtemperature and at a pressure ofaboutISOO p. s. i. g. The ethane and propane are .ad' sorbedfby .the suspended activated charcoal l and recovered therefrom by, ,ifori e);- aimple, decreasing 'the essur TtofabOutMZSO p. s. i. g. and heatinglsb :38 to vcaiiseithe ,adsorbates ethane and p'ropaneto come ofi ofithemcliarcoal adsorbent; I

l'I'hepre sent adsbrp nocss'irnafy alsolbe u s ed in therec'overy or p cation f acetyleneffrornVSachsse or Wulff y e acetyle e Ijs'trea rnsf Acetylene streams containing less 'thanIabout 15 lpe em, as t l being commercially pi-dduc'edf or 'hy ocarbons Iempl oyeld as Ho, "r; ,tliese strearns generally contain various ,propo 11s "of ace tyienqicarb on oxides, hydrogejn nitrogen and; unsaturated land/breattiratedhydrocarbons. "The etylenecanbe recovered from this streja'mfb y cont'ac t with fa slurr-y of water ari j l at d' bhimgali'm a o r a pl lf 0 m temperature andQat' jafpressure offabbiifSOipllsfi. ubst ntially, all of the acetylene finjthe gas stream 1 is adsorbed by the ch coal arid an b re il eredl therefrom preferably by a n' ofheati ligathe ,acetylene-rich adsorbentfatga o at'loi efr press'ure, e. g.,

15 p s. iQg.

In one preferred embodiment of the invention, water slurries'containing 5 percent by weight or more of activated charcoal are preferable. The adsorptive powers of the slurry increase as the quantity of charcoal in the slurry increases.

The adsorption process of the present invention can also -be"u sfed in the "removal of nitrogen from natural gas, the recoveryand purification of'ethylene from hydrogen, the purification ofvvinyl chloride in the presence ,of cetylene, 'the' purification ,of acrylonitrile in the presence of acetylene, the purification ofhydro'gen, the purification ofsynthesis gas, .the removal ofcarbon di- The slurry of"water and charcoal can alsp be used as a combination adsorption-absorption system. With this system, it is possible to obtain a fractionation be tween two dissolved gases, one more soluble in water and one ,rnorie soluble or c apable Woflbeing' adsorbed on the charcoal. Afterjhenabsorption and liadsorption, the waterand he charcoal canbeseparated from'each other by suitable','filtration meansand regenerated individually, thus giving a separation between the two gases. Systems whic h gan,be..p arated by thisfrneans are mixyres ssnt aine hydro e cyanide "and ammo i ydrogen sulfide and carbontlioxidfl,handlacrylonitrile and hydrs vmyan d 1 Since ,gertain Ichanges rnay "be .made .in ,the above process without clepa ingjrornr the scope of :the inventionher ei n i nvqlvedjit is intended that all matter contained in the above deSQIiDIiQ I lShall be interpreted as illu ra ive and 9t ;l. it ing .sense.

cla med rs:

1. A recess ,for theseparatiqn of ,ethane and propane afrorn a natural I gasstre arn ,Which comprises contacting' s a id natnral gasstreamyvith a slurry of water and activated charcoal, and recoveringjtheethine iand p q an a s rba s lsa sr ha wa .2. jAr Q 13:9 th eaa lo. ethane .and P pane from a natural gas stream whichcqmprisescontactins aid at al a stream witha slu ry o flwater f va e sh r qa ,aintain a aboutmom temp rat and tapr ssure p a lea 'sSQO pas, and rbovering t ethan and p opa ad o bed by' heating said charcoalwhile: it is rnaintain ed ,at a pressure be1o w,5.0.0 p. s.,'i. M Y

3. A process for lthe s eparation I of lett tz i ne I and I p r opanefrorn a refinery ,gas stream which comprises c ontacting said refinery gas stream with a slurry of water and activated charcoal, I and I recovering I the ethane and propanev adsorbed on said charcoal.

1 4. 'A process fort the separation of ethaneand pro- Pa o ier ea Str a ,Yr 1 h,.9t pr s a tacting said refinery gas 1 stream with I a TSII IIYQ 9f; walr a it a -L v .tmaist in abo t. 29 temlista ur Qan at a PISUIQ of at lea t spq p. s. i, g, and wv ri t e th n rmmnca orbe y. atin said charcoal whileit issnaintained at a pressure below Rsferrug syqitedw n. hat file 9 thispmnt UNITED. STATES PATENTS 2 519, 73 .lBerg Aug-22 r950 168L125 E her ngton lun 15, 1954 ggeaazrz Marple et al. Qct. I 30, 19,56 

1. A PROCESS FOR THE SEPARATION OF ETHANE AND PROPANE FROM A NATURAL GAS STREAM WHICH COMPRISES CONTACTING SAID NATURAL GAS STREAM WITH A SLURRY OF WATER AND ACTIVATED CHARCOAL, AND RECOVERING THE ETHANE AND PROPANEE ADSORBED ON SAID CHARCOAL. 